Temperature compensated resonator device having low trim sensitivy and method of fabricating the same

Abstract

A temperature compensated bulk acoustic wave (BAW) resonator device has low trim sensitivity for providing an accurate resonant frequency. The BAW resonator device includes a first electrode deposited on a substrate, a piezoelectric layer deposited on the first electrode, a second electrode deposited on the piezoelectric layer, and a mirror pair deposited on the second electrode. At least one of the first electrode and the second electrode includes an electrode layer, and a temperature compensating layer configured to compensate for a temperature coefficient of at least the piezoelectric layer.

1 . A temperature compensated bulk acoustic wave (BAW) resonator device having low trim sensitivity for providing an accurate resonant frequency, the device comprising:
 a first electrode disposed on a substrate;   a piezoelectric layer disposed on the first electrode;   a second electrode disposed on the piezoelectric layer; and   an acoustic mirror pair disposed on the second electrode,   wherein at least one of the first electrode and the second electrode comprises:
 an electrode layer; and 
 a temperature compensating layer configured to compensate for a temperature coefficient of at least the piezoelectric layer. 
   
     
     
         2 . The device of  claim 1 , further comprising:
 a passivation layer disposed on the acoustic mirror pair.   
     
     
         3 . The device of  claim 1 , wherein the temperature compensating layer is a buried temperature compensating layer encapsulated within the electrode layer and a conductive interposer layer. 
     
     
         4 . The device of  claim 3 , wherein the temperature compensating layer has tapered edges. 
     
     
         5 . The device of  claim 1 , wherein the substrate defines a cavity formed beneath the first electrode. 
     
     
         6 . The device of  claim 1 , wherein the substrate comprises an acoustic reflector formed beneath the first electrode. 
     
     
         7 . The device of  claim 1 , wherein the acoustic mirror pair comprises:
 a low acoustic impedance layer deposited on the second electrode; and   a high acoustic impedance layer deposited on the low acoustic impedance layer.   
     
     
         8 . The device of  claim 7 , wherein the low acoustic impedance layer comprises silicon dioxide (SiO 2 ), aluminum nitride (AlN), silicon carbide (SiC), boron silicate glass (BSG), silicon nitride (SiN), polysilicon, and the like 
     
     
         9 . The device of  claim 8 , wherein the high acoustic impedance layer comprises tungsten. 
     
     
         10 . The device of  claim 2 , wherein the passivation layer and the piezoelectric material are formed of the same material. 
     
     
         11 . A wafer having a plurality of bulk acoustic wave (BAW) resonator devices, separable from one another by cutting the wafer, the wafer comprising:
 a first electrode layer disposed on a substrate;   a piezoelectric layer disposed on the first electrode layer;   a second electrode layer disposed on the piezoelectric layer;   a low acoustic impedance layer disposed on the second electrode layer;   a high acoustic impedance layer disposed on the low acoustic impedance layer; and   a temperature compensating layer buried in at least one of the first electrode layer and the second electrode layer, the temperature compensation layer having a positive temperature coefficient,   wherein the temperature compensating layer enables the plurality of devices to provide substantially uniform temperature compensation, and   wherein the low and high acoustic impedance layers enable the wafer to have low sensitivity to frequency trimming, such that the plurality of devices provide substantially uniform resonant frequencies.   
     
     
         12 . The wafer of  claim 11 , further comprising:
 a passivation layer disposed on the high acoustic impedance layer.   
     
     
         13 . The wafer of  claim 11 , wherein the plurality of devices comprise a plurality of film bulk acoustic resonators (FBARs) or solidly mounted resonators (SMRs). 
     
     
         14 . A method of fabricating a plurality of bulk acoustic wave (BAW) resonator devices having low sensitivity to frequency trimming and providing substantially uniform temperature compensation, the method comprising:
 forming a first electrode layer on a semiconductor substrate on a wafer, the first electrode comprising a temperature compensating layer;   forming a piezoelectric layer over the first electrode;   forming a second electrode layer over the piezoelectric layer;   forming an acoustic mirror pair layer over the second electrode, the mirror pair comprising a low acoustic impedance layer and a high acoustic impedance layer;   forming a passivation layer over the mirror pair layer; and   frequency trimming at least one of the low acoustic impedance layer, the high acoustic impedance layer and the passivation layer to tune a resonant frequency of the plurality of BAW resonator devices.   
     
     
         15 . The method of  claim 14 , further comprising:
 separating the plurality of BAW resonator devices into singulated dies by cutting the wafer after frequency trimming the at least one of the low acoustic impedance layer, the high acoustic impedance layer and the passivation layer.   
     
     
         16 . The method of  claim 14 , wherein forming the first electrode layer comprises:
 forming a base electrode layer over the semiconductor substrate;   forming the buried temperature compensating layer over the base electrode layer; and   forming a conductive interposer layer over the buried temperature compensating layer.   
     
     
         17 . The method of  claim 16 , further comprising:
 forming a cavity between the base electrode layer electrode and the semiconductor substrate.   
     
     
         18 . The method of  claim 16 , further comprising:
 forming an acoustic reflector in the semiconductor substrate.